water activity

Water activity (a_w) is a measure of the available water in foodstuffs, ranging from 0 to 1. It's crucial for food preservation because most bacteria cannot grow in foods with a water activity below 0.91. Some bacteria, like halophilic ones, can grow at lower levels, down to 0.75.

To control water activity and prevent spoilage from microbial contamination and enzymatic activity, water can be removed through dehydration or solutes like sugar or salt can be added. This process increases solute concentration and decreases available water, inhibiting microbial growth. For example, fruit jellies and preserves are made by adding sugar and concentrating the mixture to a high solids content, preventing spoilage.123